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Hold-down offset
A setting has been added to the Default Settings page allowing input of the distance from the end of a wall or opening that a hold-down can be located. It can be saved for a particular project, and as a default value to be used for new files. A value of zero cannot be entered, so there must be some hold-down offset. The "original default setting that comes with the program is setting is 3"
Hold-downs at Contiguous Walls
The hold-down offset means that compression forces at the end of one wall are not at precisely the same location as tension forces at the end of the other. In Sizer 2004b, these forces were cancelling.
Hold-down Force Magnitude
The moment arm used for hold-down force calculations is
Vertical Force Accumulation
Where a compressive force lines up with a tension force on the floor below, such as for offset openings, the program now correctly uses the difference between these forces as the resulting force. Previously it was adding the magnitude of the tension force in one direction to the tension force in the opposite force direction.
Wind and Dead Load Combinations
The new load combination for combining wind and dead loads at hold-down locations from NBC 4.1.3.2 is used – 0.95D + 1.4W. The wind factor has changed from 1.5 and the dead factor from 0.85.
The dead load factor for dead loads combined with wind loads used for compression forces combined is 1.25, as it is not counteracting uplift.
Compression Force Load Combination (Bug CSW7-19)
The load combination 1.25D + 1.4W has been implemented for downward compression forces. Previously, the program was erroneously using the 0.9D combination.
Irregularities
If the program detects In-plane or Out-of-plane irregularities 3, 4, or 5 from Table 4.1.8.6. If there is a weak storey below, design is not allowed, if there is, all hold-down and drag strut forces use the shearwall strength rather than the applied force, according to 4.1.8.15 (2).
Anchorage restrictions
An anchorage can now be placed only where there is a tension end of a shearwall on the floor below, so that the force is distributed directly to the wall chord and the hold-down or anchorage below. Previously the anchorage force could be distributed through the shearwall from mid-segment to the shearwall ends.
A note was added to the hold-down table when hold-downs rather than anchorages were created for that purpose.
Vertical Elements for Hold-downs
Where previously an anchorage force would meets a shearwall on the floor below at mid-segment, the program creates a vertical element and a hold-down force, and transfers the force through that element further down through the structure.
Design Setting for Force Calculation
A new Design Setting allows you to choose whether to use the or the in calculating hold-down forces. The default value is applied shear, you should change this when designing connections if the design code specifies tabulated shear.
When shear capacity is required due to seismic irregularities, then this takes precedence due to